UberMedia, a Californian developer of applications that allow people to send and search messages on Twitter, said that it had been contacted for information by the Federal Trade Commission, one of America's two big competition regulators, and was co-operating.
Twitter has enjoyed explosive growth over the last two years as millions send 140-character long messages, or tweets, on the platform.
The company said this week that 200m tweets are now sent every day, and analysts argue that some of the growth has been down to applications from companies like UberMedia.
Twitter has sought to establish greater control over its platform in the last year, culminating in its $40m (£25m) acquisition in May of TweetDeck, the company behind another application that allows people to access Tweets.
Tensions are said to have increased between Twitter and the application developers that have helped drive its growth. In February, Twitter temporarily suspended UberMedia's access to the stream of Tweets.
The FTC declined to comment. Twitter could not be reached for immediate comment. -By Richard Blackden, 01 Jul 2011